St. Petersburg Bombing: The beginning of a new wave of terrorism in Russia? (part 2)

The waves of Monday's bombing in the Russian city of St. Petersburg continue to reverberate. A native of Kyrgyzstan who had Russian citizenship is believed to be responsible for the deadly metro blast which killed 14 and injured over 50. Much remains unknown about the motive: could this be retribution for increasing Russian involvement in Syria? Is the attack the beginning of a new wave of terrorism in Russia?